Controlling cold temperature partial nitritation in moving bed biofilm reactor

Abstract

Mainstream partial nitritation was studied at 10 °C in a moving bed biofilm reactor treating synthetic wastewater containing both nitrogen (≈40 mg L−1) and organic carbon at COD/N ratio ranging from 1.3 to 2.2. Three different control strategies were investigated to achieve partial nitritation. Initially, biofilm age was controlled by incorporating a media replacement strategy. Next, separately from the media replacement, oxygen limited conditions were investigated and finally pH control was incorporated together with oxygen limitation. Successful partial nitritation was achieved only by combining oxygen limitation with pH control. The average NH4-N concentration was equal to 16.0 ± 1.6 mg L−1 and average NO2-N concentration was equal to 15.7 ± 2.4 mg L−1 during steady state partial nitritation. The average residual NO3-N concentration was equal to 2.6 ± 2.2 mg L−1. The results obtained from this study prove for the first time that partial nitritation can be successfully controlled in a biofilm reactor treating wastewater with low nitrogen concentration, relatively high COD/N ratio and at low temperature. An algorithm for dynamic process control of partial nitritation has been also developed.